Background and purpose: In Iran, wheat is one of the main cereals for human consumption. Wheat grains containing zearalenone can cause genital problems and reproductive disorders in domestic animals. In human, episodes of breast enlargement in young boys and sexual precocity have been reported. This toxin may therefore have a role in hormonal balance and mammary cancer in regions with high zearalenone ingestion. In this study the incidence of zearalenone in wheat samples from Mazandaran warehouses were investigated.Material and methods: A total of 118 wheat samples (1 kg each) were randomly collected from all 12 warehouses of Mazandaran province. Competitive microtitre plate enzyme immunoassay for the quantitative determination of zearalenone was used according the manufacturer instructions (Riedel-de Haen Sigma-Aldrich Laborchemikalien GmbH). Results: Zearalenone was found in 81% of samples and 64.4% of samples contained >200 μg/kg of this toxin. The minimum levels of zearalenone were 29 μg/kg. All of the warehouses were positive for the presence of zearalenone. 50-100% of samples in each of the warehouses had >200 μg/kg contamination of zearalenoneConclusion: Our results showed a high percentage and levels of contamination of wheat samples with zearalenone. With regard to proposed standards given by the Standard Administration of Iran, under which the content of zearalenone should not exceed 200 ppb in food products, 64.4% of samples meet these criteria.